When a set of data encompasses geographic location as the reference component, it is referenced to as geospatial data. It represents some information about a specific location or over a range of a given location. The location can range from a specific point to a larger area. Oftentimes, GIS and geospatial data are interchangeably used.
GIS is a programmatic system that creates, stores and analyses geospatial data.
View the original blog here Understanding Geospatial Data
To know more about, how geospatial data can be used using postgis please take a gander at the follow up article: Getting started with PostGIS.